The invention relates to improvements in apparatus for admitting metered quantities of flowable bulk material into discrete bags or other types of receptacles, especially into open bags or valve type bags. More particularly, the invention relates to improvements in apparatus for filling bags or other types of receptacles (hereinafter called bags for short) with metered quantities of bulk material which is caused or permitted to enter discrete bags by gravity flow. The invention also relates to a method of adjusting bag filling apparatus the above outlined character in order to ensure that discrete bags are filled with metered quantities of flowable bulk material within shortest possible periods of time.
Apparatus of the above outlined character are disclosed, for example, in Schwake et al. U.S. Pat. No. 3,474,836 and in published German patent application No. 2 020 356 to Kopp. As a rule, an apparatus which serves to fill bags with granular, pulverulent or other flowable bulk material comprises a weighing or metering vessel as a means for gathering successive metered quantities of flowable material, depending upon whether such metered quantities are to be gathered by weight or by volume. It is customary to dump a metered quantity of bulk material from the weighing vessel or from the metering vessel into a normally funnel-shaped hopper below the gathering station. The outlet at the bottom end of the hopper is connected with the open upper end of a gravity flow duct the open lower end of which is connectable with discrete open bags or valve type bags. Successive metered quantities of bulk material are caused or permitted to descend in the duct by gravity flow on their way into discrete bags. If the bags are valve type bags, the duct normally constitutes a suitably designed pipe or a system of pipes which are known as gravity flow pipes. The duct is similar if the apparatus is designed to admit metered quantities of bulk material into open bags, except that the dimensions of the gravity flow pipe or pipes are normally larger, depending on the size of the material-admitting openings of the bags.
The aforementioned published German patent application of Kopp discloses a bag filling apparatus wherein a conical flow regulating device which constitutes a flow restrictor) is disposed at the downwardly converging lower end of the hopper directly or closely above the open upper end of the gravity flow duct. The flow regulating device is movable up and down to thereby increase or reduce the cross-sectional area of the passage or path for the flow of a metered quantity of bulk material from the hopper into the duct. Thus, an adjustment of the rate of gravity flow of bulk material into an open or valve type bag at the lower end of the duct involves an upward or downward movement of the flow regulating device in the hopper. It is desirable to select the level of the flow regulating device in such a way that a metered quantity of flowable bulk material can descend into and in the gravity flow duct without risking any clogging of the duct because this would entail a pronounced lengthening of the period of time which is required to transfer a metered quantity into the bag at the lower end of the duct. In many instances, the duct is an elongated slender cone the diameter of which decreases in a direction from the upper end toward the lower end so that the likelihood of clogging in or close to the lower end increases as the rate of admission of flowable material into the upper end of the duct increases. Clogging is normally attributable to internal friction within the descending stream of flowable bulk material and/or to friction between the particles of the descending stream and the internal surface of the duct. It is well known that the period of time which is required to complete the admission of a metered quantity of bulk material into a bag by gravity flow through an upright or substantially upright duct increases dramatically if the rate of admission of material into the duct is sufficiently high to cause partial or complete clogging of the duct, particularly close to the lower end of a conical duct. In other words, the output of a bag filling apparatus is drastically reduced if the rate of flow of bulk material in the duct is too high so that the duct is clogged in the course of a bag filling operation.
The length of periods which elapse to complete a filling operation is dependent upon several non-variable parameters, such as the consistency of flowable material and the dimensions of the bags, as well as on one or more variable parameters, such as the rate of evacuation or expulsion of air from the duct and/or from the bags. In accordance with presently prevailing techniques, the flow regulating device is adjusted by hand based on the expertise of the person in charge. The arrangement is such that the person in charge selects a certain rate of gravity flow, and the thus selected adjustment is thereupon adhered to for the filling of a shorter or longer series of bags with metered quantities of flowable bulk material. In other words, the flow regulating device is adjusted prior to start of a continuous bag filling operation and the flow regulating device thereupon remains in the initially selected position. This is highly unlikely to result in the filling of bags at an optimum rate, i.e., in such a way that each bag is filled with a metered quantity of flowable bulk material within the shortest possible period of time.
It is customary to put a single person in charge of supervising the operation of an entire battery of automatic bag filling apparatus. In such bag filling plants, the person in charge of supervising the operation of several discrete automatic bag filling apparatus would be incapable of continuously monitoring the operation of each individual apparatus for the purpose of adjusting the flow regulating device in order to ensure that the bag filling operation will be carried out with maximum efficiency. As a rule, the person in charge is stationed at a certain distance from the battery of automatic bag filling machines in order to ensure that such person can readily supervise the operation of all machines. Therefore, a relatively long interval of time elapses to carry out an adjustment if an apparatus fails to operate properly, particularly if the lower end of a downwardly tapering conical duct happens to be clogged with flowable bulk material. Such clogging is also known as choking.
The output of a bag filling apparatus is higher if the distance of the adjustable flow regulating device from the bag (i.e., from the lower end of the gravity flow duct) is increased. In order to further increase the output, many presently known bag filling apparatus are operated in such a way that the contents of a weighing vessel or metering vessel are evacuated (i.e., admitted into the gravity flow duct) before an empty bag is affixed to the lower end of the duct. This is possible if the duct is long so that a certain interval of time elapses before the lower end of a stream of metered quantity of bulk material descends from the upper end into and beyond the lower end of the duct. However, the height or length of the duct cannot be increased at will, not only because such lengthening contributes significantly to the cost of the duct but also because the overall height of the bag filling apparatus must be kept within certain limits in order to ensure that such apparatus can be confined in available factory buildings.
In many instances, the aforementioned conical flow regulating device (which is installed in the hopper in such a way that its apex is located at the upper end) is movable between two different positions, i.e., between two different levels. This renders it possible to discharge the bulk material at a higher rate (in the upper position of the flow regulating device) and at a lower rate (in the lower position of the flow regulating device). The ode of operation is normally such that the flow regulating device is held in the lower position at the time the contents (i.e., a metered quantity of a weighing or a metering vessel) are dumped into the hopper for the flow regulating device. This is considered to be desirable and advantageous in order to avoid unobstructed descent of a stream of metered quantity of flowable bulk material from the vessel directly into the duct and thence into the sack or bag at the lower end of the duct. Thus, the freshly dumped metered quantity of bulk material is supposed to impinge upon the conical surface of and to gather above the flow regulating device prior to entering the upper end of the duct. Once the entire metered quantity of flowable material has been transferred into the hopper and the rate of flow around the flow regulating device and into the duct has settled so that the descending material is accelerated from zero speed on its way into and through the duct and thence into a bag at the lower end of the duct, the flow regulating device is lifted to its upper position to permit the bulk material which has gathered in the hopper to descend into the duct at the higher of the two rates. The just discussed mode of operation is being resorted to irrespective of whether the apparatus is set up to fill open bags or valve type bags.